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September 24, 2010

Study Measures Size Of Gulf Oil Spill

by Sam Savage

In the first independent and peer-reviewed analysis of the Gulf of Mexico oil spill, scientists from Columbia University have determined that 4.4 million barrels of petroleum leaked into the water following the sinking of the Deepwater Horizon rig in late April.

The study, which was the work of Columbia researchers Timothy J. Crone and Maya Tolstoy, was published online in the September 23 edition of the journal Science. As part of their work, Crone and Tolstoy analyzed underwater video footage of the busted Macondo 252 well, and found that it leaked at least 56,000 and 68,000 barrels daily between April 22 and July 15.

According to AP Science Writer Seth Borenstein, Crone and Tolstoy calculated that nearly 185 million gallons of oil spilled during the course of the summer. In comparison, Borenstein notes that the federal government's most recent estimate was more than 12 million gallons lower.

"We wanted to do an independent estimate because people had the sense that the numbers out there were not necessarily accurate," Crone, the study's lead author and a marine geophysicist at the university's Lamont-Doherty Earth Observatory, said in a statement Thursday. According to that press release, officials at Columbia University also noted that the Gulf oil spill "is now acknowledged as the largest marine oil accident ever."

"The new study divides the flow rate into two periods: April 22 to June 3, when oil spurted from a jagged break in the riser; and after June 3, when the riser was cut, and oil temporarily spewed into the ocean unimpeded," the press release reports, adding that Crone and Tolstoy discovered that video from the first period showed an average flow of 56,000 barrels per day and the rate during the second increased to approximately 68,000 barrels daily, with an error margin of plus or minus 20%.

The technique used by Crone and Tolstoy in the study is known as optical flow velocimetry. According to ScienceNews, "In this approach, the volume of a roiling plume is estimated by using video or a series of photos to measure the movements of a host of distinguishing features over a short period of time. Computers can then calculate likely flow volumes based on the plume's size and density."

On Sunday, officials from BP and the U.S. government confirmed that the sunken oil well had finally been permanently sealed with cement, some five months after the environmental catastrophe began with an explosion onboard the Deepwater Horizon that killed 11.

"We can finally announce that the Macondo 252 well is effectively dead," Thad Allen, the retired Coast Guard Admiral who had led the American government's response to the natural disaster, told AFP shortly after the sealing of the well. "Additional regulatory steps will be undertaken but we can now state, definitively, that the Macondo well poses no continuing threat to the Gulf of Mexico."

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Image 1: The researchers used high-resolution video clips of flow from the Deepwater Horizon well to measure volume. Credit: Courtesy US Senate Committee on Environment and Public Works

Image 2: Study author Timothy Crone (left) prepares to deploy a camera designed to monitor the flow of hydrothermal vents off the US Pacific northwest. He used similar technology to estimate the flow of the gulf oil spill. Credit: Photo by Carlos Sanchez, OOI-RSN Enlighten'10 Cruise, University of Washington